1. Field of the Invention
The invention relates to a baseline drift canceling method to remove a baseline drift signal in a bioelectric signal.
2. Description of the Related Art
When measuring the bioelectric signal of a human body, two sensor patches are usually applied for sensation of the human body. Take the electrocardiograph machine for example, the electrocardiograph machine senses the bioelectric signal from sensor patches on the chest or hands of the human body. However, the sensed bioelectric signal is easily affected by the breathing, movement, skin resistance or sweat on the skin of the human body. This may cause the baseline to drift or wander and when the baseline drift is too large, a resulting output signal may be saturated and the bioelectric signal would be inaccurate.
One conventional method to solve the issue of a baseline drift is to directly filter out the baseline drift signal, such as that disclosed in U.S. Pat. No. 5,318,036. The method disclosed by U.S. Pat. No. 5,318,036 filters an output from a front-end filter by a digital high pass filter in a microprocessor to remove the baseline drift. Another conventional method estimates a baseline drift signal by a microprocessor and subtracts the estimated baseline drift signal from the bioelectric signal. The baseline estimation method is disclosed in U.S. Pat. No. 6,280,391 and U.S. Pub. No. 20070078354. Another baseline estimation method is disclosed in U.S. Pat. No. 6,881,191 to estimate the baseline drift signal by curve fitting. However, the described baseline drift canceling methods require complicated circuitry or increased hardware and/or software, thus, delaying results. Additionally, in certain cases, the baseline drift tolerance (the voltage range of the baseline drift/the amplitude of vibration of signal) for the described baseline drift canceling methods are limited.